The present invention relates to a light curtain generating device for sensing the entry of a human body or the like into a designated danger area, and in particular to a light curtain generating device which can adjust the length of the light emitting and receiving pillar assemblies, number of light beams and pitch of the light beams according to the width of the danger area, the diameter of the smallest possible object that is desired to be detected, and so on, in a flexible manner.
As well known in the art, an optical curtain generating device of this kind comprises a light emitting pillar assembly accommodating an array of light emitting units within a pillar case and a light receiving pillar assembly accommodating an array of light receiving units within a pillar case, the light emitting pillar assembly and light receiving pillar assembly being placed opposite to each other so as to form a light curtain for detecting an object between the pillar assemblies.
The arrays of light receiving and emitting units accommodated in the pillar cases are typically formed by combining a plurality of multi-beam optical modules each having a unit number of light beams (such as four, eight and sixteen light beams). Each multi-beam optical module comprises a number of optical elements (a light emitting element and a light emitting lens in the case of a light emitting unit, and a light receiving element and a light receiving lens in the case of a light receiving unit,) corresponding to the unit number of light beams which are integrally incorporated in a plastic holder which fixes the pitch of the light beams. Such a multi-beam optical module is disclosed in Japanese patent laid open (kokai) publication No. 10-74432.
However, according to such a conventional light curtain generating device, because the length of the light emitting and receiving pillar assemblies, number of light beams, pitch of the light beams and so forth are determined by the combination of multi-beam optical modules each having a fixed number of light beams and a fixed light beam pitch, the following problems are known to exist.
(1) Because the number of light beams which matches the width (Al) of the designated danger area cannot be selected at will as illustrated in FIG. 18, the length of the light emitting and receiving pillar assemblies (Z6 and Z7) may be longer than necessary. In such a case, the light emitting and receiving pillar assemblies (Z6 and Z7) may extend beyond the machine (such as a stamp forming machine Z1), and occupy more space than desired. Also, the unnecessary light beams (the area of unused light beams A2) mean a waste in cost. It is also possible that an object outside the designated danger area may be detected, and the machine may be turned off unnecessarily. On the other hand, if the light emitting and receiving assemblies are selected to fit within the designated danger area (A1), the presence of insensitive areas in the upper and lower ends may prevent the necessary width for detection from being attained.
In FIG. 18, Z1 denotes a stamp forming machine, Z2 denotes a front opening, Z3 denotes an upper block, Z4 denotes a lower block, Z5 denotes a stamp forming zone, Z6 is a light emitting pillar assembly, and Z7 denotes a light receiving pillar assembly.
(2) Because the only possible light beam pitches are the basic pitch of the light beams inherent to the particular multi-beam optical module and a multiple thereof, the light beam pitch cannot be optimized for the particular diameter of the smallest possible object that is desired to be detected.
(3) Because the optical module has a plurality of light beams, it tends to be large in size and highly complex so that the assembly process is hard to be mechanized.
(4) Because the optical module has a plurality of light beams, a large metallic die assembly is required for the fabrication thereof, and the cost for the metallic die assembly increases.
(5) Because the optical module has a plurality of light beams, its length increases, and ensuring the required optical precision becomes difficult because the warping of the molded product becomes difficult to control as the length of the molded product increases.
(6) Because various kinds of optical modules are needed for different light beam pitches, stocking them creates a problem, and the cost for the metallic die assemblies is therefore high. For instance, if the light beam pitches include 15 mm and 20 mm, a separate metallic die assembly is needed for each of them. If the light beam pitches include 15 mm and 30 mm, and a 30 mm pitch is achieved by using the 30 nun pitch optical module by enabling only every second light beam, there are unused optical components (such as lenses) between each pair of adjacent light beams that are used, and the cost for the unused optical components will be wasted.
The present invention was made in view of such problems of the prior art, and a primary object of the present invention is to provide a light curtain generating device which can be selectively fabricated so as to be adjustable with respect to the length of the light emitting and receiving pillar assemblies, number of light beams and pitch of the light beams according to the width of the danger area, the diameter of the smallest possible object that is desired to be detected, and so on, in a flexible manner.
A second object of the present invention is to provide a light curtain generating device which can readily adapt itself to each particular application at low cost.
A third object of the present invention is to provide a light curtain generating device which can readily adapt itself to the desired length of the detection area in a highly precise manner.
The light curtain generating device of the present invention comprises a light emitting pillar assembly accommodating an array of light emitting units within a pillar case and a light receiving pillar assembly accommodating an array of light receiving units within a pillar case, the light emitting pillar assembly and light receiving pillar assembly being placed opposite to each other so as to form a light curtain for detecting an object between the pillar assemblies.
The light emitting unit array and light receiving unit array received in the respective pillar cases comprise a group of single-beam optical modules.
Thus, the light emitting and receiving pillar assemblies can be fabricated so as have a length which is adjustable by each single light beam so that the device can be adapted to each particular width of the designated danger area in a flexible manner.
According to the present invention, each opposing pair of a light emitting unit and a light receiving unit may perform a detecting action in a prescribed order.
Thus, a proper detecting action can be ensured without risking interferences between adjacent optical modules.
According to the present invention, each single-beam optical module may consist of a light emitting unit or a light receiving unit comprising a lens, an optical element and a holder integrally incorporated with them so as to align them with a prescribed optical axial line.
The optical element consists of a light emitting element in the case of a light emitting unit and a light receiving element in the case of a light receiving unit.
Thus, the handling of the single-beam optical module during the fabrication process can be simplified.
According to a preferred embodiment of the present invention, the holder may be made of plastic material.
Thus, only one kind of metallic die assembly is required for the fabrication process, and the cost for the metallic die assembly can be minimized.
The single-beam optical modules serving as the light emitting units or as the light receiving units may be identical to one another. Thereby, the management and fabrication of the single-beam optical modules can be simplified.
According to the present invention, the lens and optical element may be joined to the plastic holder by snap fit arrangements.
Thus, the assembly of each single-beam optical module can be mechanized, for instance, by using a robot.
According to the present invention, each group of single-beam optical modules may comprise an optical module block including a plurality of single-beam optical modules arranged in a single row by being attached to a metallic plate having a prescribed length.
Thus, a plurality of single-beam optical modules can handled in a single body, and they may be retained by a metallic plate. Therefore, a plastic holder for retaining them is not needed, and no cost is required for a metallic die assembly for molding such a plastic holder. Furthermore, because any desired mounting pitch of the single-beam optical modules can be readily achieved by a simple metal working process, and the change in the light beam pitch can be effected at low cost and in a flexible manner.
According to the present invention, each single-beam optical module forming the optical module block may be attached to the metallic plate at a side of the single-beam optical module extending in parallel with the optical axial line.
Thus, the optical axial line and the metallic plate are in parallel to each other, and the accuracy of the optical axial line can be ensured more easily as compared with the case where each single-beam optical module is supported at a bottom surface thereof.
According to the present invention, each single-beam optical module forming the optical module block may be attached to the metallic plate by a snap fit arrangement.
Thus, the assembly of each single-beam optical module can be easily mechanized, for instance, by using a robot.
According to the present invention, the device may further comprise a circuit board having a plurality of optical element mountable, and signal processing means for electrically and selectively disabling the optical element mountable positions.
Thus, by omitting one out of a certain number of single-beam optical modules, an optical pitch which is a multiple of the basic light beam pitch can be accomplished, and no components will be wasted between adjacent light beams as was the case with the conventional arrangement.
According to a particularly preferred embodiment of the present invention, each pillar assembly comprises at least two base frames arranged in series along a length of the pillar assembly each defining mounting positions for single-beam optical modules, and a plurality of single-beam optical modules mounted in the mounting positions of the base frames. This embodiment allows a free selection of the arrangement of the single-beam optical modules.
For instance, the mounting positions of the two base frames may have different pitches. Additionally or alternatively, the two base frames may have different numbers of mounting positions and/or different lengths.